There are essentially two
ways contamination occurs. One is called point source contamination. For example, an oil spill is a point source
contamination, as there is a known, recognizable source responsible for the contamination. The second
way is called non-point source contamination. This occurs when no obvious, recognizable source of contamination
is apparent. Pesticides washed by rainfall from farmers' fields into nearby rivers is a common example of non-point
source contamination. Here is a list of examples of both types of contamination.

Typically, there
are three types of water contamination. These include agricultrual , industrial , and municipal contamination. For
the purposes of this website, oil spills will be separated from the industrial category and placed into their own
category. This will make four cateories of water contamiation: agricultural, municipal, industrial, and oil
spill contamination.

Agricultural contamination

Agricultural contamination refers to
the contaminants found in the surface water and/or groundwater as a result of large-scale livestock and poultry farming
as well as from farmers' croplands. A classic example of agricultural contamination is pesticides being washed into
rivers and streams by rainfall.

Most agricultural contaminants that
enter the groundwater are nitrates and pesticides. Pesticides, designed to protect the farmer's crops from
pesky insects, are applied directly to the soil by the farmers. However, if these pesticides are not applied in
the proper conditions or if the field is improperly managed, the pesticides leach through the soil and into the groundwater.
Contamination due to pesticides, although found in almost every American state, occurs much less frequently than nitrate
contamination. Nitrate contamination is much more common because it is very soluble in water. This means that
it can leach through wet or moist soil and into the groundwater very easily.

The nitrates
that are causing the contamination can come from a number of sources such as: nitrogen rich fertilizers, animal manure,
and nitrogen-fixing plants such as legumes. There are certain conditions that will be more likely to cause
a contamination than others. The most common contamination-causing conditions are: improper timing of application
of fertilizer or manure, excessive fertilizer or manure, and over irrigation.

Crop Spraying

This is a picture of a farmer spraying his crops with pesticides

Municipal Contamination

Municipal contamination
refers to the wastewater that comes from our homes and small businesses. Due to advanced filtration systems, many
of the contaminants are filtered out or broken down before the water is returned to the drinking water supply.
However, these barriers do not stop everything. Sometimes, a contaminant survives the filtration system and appears
in the drinking water. This contaminant could have originated from almost anywhere. Take a minute to consider
what kinds of things you dump down your sink on a daily basis.

A good example
of a municipal contamination would be Lake Huron. Recently, several beaches on Lake Huron were closed due to E.
coli contamination. E. coli is a bacteria that is found in the stomach and intestines of humans and cattle.
When it is found on a beach, that is a good indication that somehow, fecal matter has found its way into the lake water, which
raises serious health concerns. If people were to drink the water containing the e. coli, they would become very
sick and could possibly die.

The seriousness
of e. coli contamination was demonstrated in Walkerton, Ontario in May 2000. Filtration of the town's
drinking water was improperly managed and as a result, e. coli made its way into the drinking water. When people
drank their tap water as they usually did, they were unknowingly ingesting e. coli bacteria. By the time it was over,
seven people had died and over 2,000 people were sick. This clearly demonstrates what can happen when the filtration
process is neglected. The best defence against municipal contamination is an up-to-date, carefully monitored water
filtration system.

Water Treatment Facility

This is a picture of a water treatment facility. Here, water is filtered to eliminate contaminants.

Industrial Contamination

Industrial contamination
is any contamination that occurs as a result of the dumping of industrial waste. An example of industrial contamination
occurred in Ville Mercier, Quebec. Industrial waste was dumped into lagoons in an old gravel pit. This went on
for many years until eventually, water supplies of thousands of surrounding residents were made unusable. To restore
the area to its original condition, water had to be pumped into the area from 10 km away.

Although awareness has increased, the problem
of industrial contamination has been increasing. This is mainly due to the increase in number and toxicity of the products
used in industrial processes. Most industrial contamination occurs as point source contamination, with the contaminants
entering the water through direct discharges. Most of the industrial contamination that occurs today is a result
of dumping toxic wastes and chemicals and raw sewage directly into our lakes and rivers. There would also
be a small amount of contamination produced indirectly through the smoke stacks. The contaminants would enter the atmosphere
and could be carried far away from the factory and fall to the ground with rain.

Chromium Puddle

Chromium leaked from industrial sites into a parking lot where it mixed with the water. (New Jersey)